When you were a beginner at Java, did you by chance already know how to program in an imperative or OO manner? I find it highly unlikely that anyone unfamiliar with imperative/OO programming in general would get any benefit from reading Java libraries. If you want to get benefit from reading Haskell libraries, just like in Java, you need to learn how to program in the paradigm. Not just "have casual encounters" with it, not just reading things about it, but actually learn the thing.
A direct analogy to what you're saying: When I was studying French, I was able to read articles above my level and get a decently good idea of what they said. Now I'm studying Chinese, and I can't tell at all what characters mean! This should not be surprising. French is very similar to English, where Chinese is very different. Of course picking things up in the latter will be more difficult. It would be absolutely absurd to blame the Chinese language for that.
A direct analogy to what you're saying: When I was studying French, I was able to read articles above my level and get a decently good idea of what they said. Now I'm studying Chinese, and I can't tell at all what characters mean! This should not be surprising. French is very similar to English, where Chinese is very different. Of course picking things up in the latter will be more difficult. It would be absolutely absurd to blame the Chinese language for that.